The diffusive behavior of D in 5N-purity single crystals was studied at 670 to 1270C. The results could be described by:

D (cm2/s) = 5.27 x 10-3 exp[-9.24(kcal/mol)/RT]

L.Katz, M.Guinan, R.J.Borg: Physical Review B, 1971, 4[2], 330-41